CS:GO Help Thread

How do these "fast flashbang" works?

Like, some players throw the flash on the edge of something (The part that I already fail) and then it goes, example given, right into the B spot from Dust II.

How do they do this? <_> They walk from CT to B (Dust II) and throw the flash to the edge below the window of B. If I try it I always fail, no matter if I move or if I don't